App.js

/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 * @flow
 */

import React, { Component } from 'react';
import {
  StyleSheet,
  Text,
  View
} from 'react-native';

import Camera from 'react-native-camera'

export default class App extends Component {
  render() {
    return (
      <View style={styles.container}>
        <Camera
          ref={(cam) => {
            this.camera = cam
          }}
          style={styles.view}
          aspect={Camera.constants.Aspect.fill}>
            <Text 
            style={styles.capture} 
            onPress={this.takePicture.bind(this)}>
              [CAPTURE_IMAGE]
            </Text>
        </Camera>
      </View>
    );
  }

  takePicture() {
    const options = {}

    this.camera.capture({metadata: options}).then((data) => {
      console.log(data)
    }).catch((error) => {
      console.log(error)
    })
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    flexDirection: 'row'
  },
  view: {
    flex: 1,
    justifyContent: 'flex-end',
    alignItems: 'center'
  },
  capture: {
    flex: 0,
    backgroundColor: 'steelblue',
    borderRadius: 10,
    color: 'red',
    padding: 15,
    margin: 45
  }
});